1. Field of the Invention
The present invention relates to the assembly of semiconductor packages and, in particular, to an apparatus and method for efficiently assembling semiconductor packages.
2. Background of Related Art
Semiconductor chips are used in various electrical and electronic products, such as cellular phones and computers. The chips are able to interconnect millions of transistors on a surface with an area as small as 1 centimeter squared, thereby enabling designers to integrate very sophisticated and complex functions in an efficient physical device. In order to create a suitable electrical interface for the tiny chips and the products in which they are used, manufacturers use various techniques to attach the chips to intermediate mediums that are capable of forming electrical connections with both the chips and the products.
These intermediate mediums typically are nonconductive rectangular plates, sometimes called substrates, that have conductive pads on both plate surfaces. A semiconductor chip is attached to one plate surface of a substrate and forms an electrical connection with the conductive pads on that plate surface. A conductive material, such as solder, is attached to the conductive pads on the other plate surface to facilitate the forming of an electrical connection with the product in which the chip is used. The conductive pads on both sides of the plate also form electrical connections with each other, thus completing the electrical connection between the semiconductor chip and the product. The combination of the substrate and the semiconductor chip is typically referred to as a semiconductor package, a ball grid array (xe2x80x9cBGAxe2x80x9d) package, or a chip scale array package (xe2x80x9cCSPxe2x80x9d), and as a unit, is ready to be used in its designated product.
During the production of semiconductor packages, manufacturers typically attach the conductive material and the semiconductor chip to the substrate in several separate steps. For example, a manufacturer might place solder, in the form of individual solder balls, onto a substrate so that the solder balls are aligned with respective conductive pads, place the substrate into a heating oven to melt the solder balls onto the conductive pads on that side of the substrate, remove the substrate with the attached solder, flip the substrate over, place the semiconductor chip with pre-formed solder bumps onto the other side of the substrate so that the pre-formed solder bumps on the semiconductor chip are aligned with the conductive pads on the substrate, and send the package into a heating oven again, to attach the semiconductor chip to the substrate. Alternatively, a manufacturer might practice the same process in reverse, i.e., place the semiconductor chip with solder bumps on the substrate, heat the chip and substrate, flip the substrate over, place solder balls onto the substrate, and send the package into the heating oven again, to attach the solder balls to the substrate.
Either process requires two separate passes through the heating oven, first to melt the solder balls onto the conductive pads on one side of the substrate, and then to attach the semiconductor chip to the other side of the substrate. The use of two separate passes is necessary due to the fact that something is being attached to both sides of the substrate and gravity is affecting the overall assembly. If the solder balls were placed on the top surface of the substrate, for example, and then the substrate was flipped over without first being passed through a heating oven, the solder balls would fall off. Similarly, if the semiconductor chip was placed on the top surface of the substrate and then the substrate was flipped over, the semiconductor chip would fall off.
While necessary, the double pass through the heating oven is more costly and time consuming to the manufacturer than a single pass would be. If, for example, more than one heating oven is used for the two separate heating passes, more capital expenditure, from the manufacturer""s standpoint, is required. A manufacturer would like ideally to use as few machines as possible. The use of multiple passes through heating ovens also causes additional handling of the products, decreases throughput, and increases idle inventory. All of these factors contribute to the costliness of the manufacturing process. The extra pass through a heating oven also increases the likelihood of damaging the substrate, further complicating and retarding the process by lowering package reliability.
In addition, in conventional processes, the step of attaching the individual solder balls to their respective conductive pads on the substrate requires precision. The requisite amount of precision makes this step in the process of manufacturing semiconductor packages also expensive and time consuming. There exists a need, therefore, for an apparatus and method for more efficiently manufacturing semiconductor packages by reducing the number of required passes through a heating oven from two to one and by facilitating the attachment of solder to conductive pads on a substrate.
In order to overcome the disadvantages of the prior art and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention comprises an apparatus for attaching conductive materials to conductive pads on a substrate, comprising: a plate having pockets located to align respectively with the conductive pads on the substrate, so that when the conductive materials are placed into the pockets and the substrate is placed onto the plate, the conductive materials contact the conductive pads on the substrate. Preferably, the pockets extend partially through the substrate.
In another preferred embodiment, there is provided an apparatus for attaching conductive materials to conductive pads on a substrate, comprising: a plate having pockets arranged in a pattern so that one group of the pockets align respectively with the conductive pads of one substrate, and so that at least one other group of the pockets align respectively with the conductive pads of at least one other substrate having conductive pad locations different than conductive pad locations on the one substrate.
In another preferred embodiment, there is provided an apparatus for attaching conductive materials to conductive pads on one side of a semiconductor substrate having other conductive pads on another side thereof, and for attaching a semiconductor chip to the other side of the semiconductor substrate, the semiconductor chip having solder bumps on one side to complement and connect with the other conductive pads on the other side of the semiconductor substrate, the apparatus comprising: a pallet having pockets to receive the conductive materials; a pick-and-place mechanism for aligning and placing the semiconductor substrate onto the pallet so that at least a portion of the pockets on the pallet are aligned respectively with the conductive pads on the one side of the semiconductor substrate, and for aligning and placing the semiconductor chip onto the semiconductor substrate so that the solder bumps on the one side of the semiconductor chip are aligned respectively with the other conductive pads on the other side of the semiconductor substrate; and a heating device for simultaneously heating the pallet, conductive materials, semiconductor substrate, and semiconductor chip so that the conductive materials attach permanently to the conductive pads on the one side of the semiconductor substrate and the semiconductor chip attaches permanently to the other side of the semiconductor substrate.
In another preferred embodiment, there is provided a method of attaching conductive materials to conductive pads presented at a generally flat substrate, comprising the steps of: providing a plate having a plurality of pockets arranged so that one of the pockets corresponds in location to each of the conductive pads; placing the conductive materials into selected pockets; and placing the substrate onto the plate so that the conductive materials contact and attach to the conductive pads on the substrate.
In another preferred embodiment, there is provided a method for attaching conductive materials to conductive pads on one side of a semiconductor substrate having other conductive pads on another side thereof, and for attaching a semiconductor chip to the other side of the semiconductor substrate, the semiconductor chip having solder bumps on one side to complement and connect with the terminals on the other side of the semiconductor substrate, the method comprising the steps of: providing a plate having pockets; placing the conductive materials into selected pockets; placing the substrate onto the plate so that the conductive pads on the one side of the substrate are aligned respectively with the selected pockets on the plate; placing the semiconductor chip onto the substrate so that the other conductive pads on the other side of the substrate are aligned respectively with solder bumps on the semiconductor chip; and simultaneously heating the plate, conductive materials, substrate, and semiconductor chip so that the conductive materials attach permanently to the conductive pads on the one side of the substrate and the semiconductor chip attaches permanently to the other side of the substrate. Preferably, the conductive materials may comprise solder paste, solder balls pre-mixed in flux, solder balls coated with tacky flux, or solder balls coated with liquid flux.
In a further embodiment, there is provided the step of placing onto the plate a stencil having holes that register with the selected pockets on the plate and with conductive pads on the substrate; and spreading the conductive materials across the stencil so that the conductive materials moves through the holes of the stencil into the selected pockets of the plate.
In other embodiments, there are provided the steps of removing the combined conductive materials, substrate, and semiconductor chip from the plate; applying a non-conductive bonding-material substance between the substrate and the semiconductor chip; cleaning the combined conductive materials, substrate, semiconductor chip and non-conductive bonding-material substance; and/or applying a non-conductive bonding abrasive-resistant material over the combined conductive materials, substrate, semiconductor chip and non-conductive bonding-material substance.
In another preferred embodiment, there is provided an apparatus for attaching conductive materials to conductive pads on a substrate, comprising: a plate having pockets, at least some of the pockets being located to align respectively with the conductive pads on the substrate so that when the conductive materials are placed into the at least some of the pockets and the substrate is placed onto the plate, the conductive materials contact and attach to the conductive pads on the substrate.